This proposal is a three-year planning and feasibility study to develop and test a six-year, full-scale intervention program in coordination with other selected field centers in response to the NHLBI RFA titled: "Primary Prevention of Obesity in American Indians/Alaska Natives." Native American communities have high rates of several chronic diseases, most notably diabetes and obesity. The increase in obesity in the U.S. population, and particularly in the Native American population, demonstrates the need for comprehensive intervention studies designed to reverse this national trend. For Pima and Tohono O'odham Native American participants in this field center, the early onset of obesity in preadolescent children has increased to alarming levels with the mean body mass index in 8 to 10 year-old children already at or above the 95th percentile for the general U.S. population. We have estimated the body fat content of these children and found that about 50% are obese as compared to only 5-10% of the U.S. population in this age group. In this proposal we have developed a multidisciplinary intervention program that is school, family, and community-based and that draws from social learning theory and adoption-diffusion models. The program has been adapted to the Native American community based on programs previously developed at the Gila River and Tohono O'odham Indian communities. The intervention program is designed to increase physical activity levels and self-esteem and to modify dietary intake and includes an out-of-school as well as in-school curriculum, a comprehensive summer program, and programs for the school staff, parents and community. During the first year we propose a cultural analysis to further select and adapt curricula for this population. During the second and third years we propose extensive pilot testing of the curricula in physical fitness, psychosocial development and nutrition education. In addition, we will assess the reliability of both primary (body composition) and secondary endpoints (measurements of physical activity and fitness, dietary intake and selected psychosocial measurements). For the full-scale, six-year intervention study, we propose a randomized clinical trial and four-year intervention program for second, third, fourth and fifth graders using 300 children in each of two cohorts. Schools of similar size and other characteristics will be paired and randomly assigned to either an obesity intervention arm or control (alcohol and substance abuse) program, thus enabling all children to receive prevention education. Our proposed intervention program includes professionals working at the Gila River, Tohono O'odham and Salt River Indian communities, scholars at The University of Arizona and consultants from the National Institute of Diabetes and Digestive and Kidney diseases, the Cleveland Clinic Foundation, the Medlantic Research Institute and the National Institute of Alcoholism and Alcohol Abuse. These individuals collectively provide expertise in the areas of health promotion, school-based intervention programs, nutrition education and assessment, body composition assessment, physical activity assessment and fitness education, substance abuse, clinical psychology, pediatrics, epidemiology, and biostatistics.